Evidence for field induced trapping of a defect dipole in MgO-crystals

A thermally stimulated depolarisation peak from a MgO single crystal shows a peculiar response to sequences of poling conditions. A field induced mechanical relaxation which fixes (or frees) an anisotropic defect dipole is suggested.     

The three reorientation processes of O-2 centres in unstressed alkali halide crystals

Measurements of the reorientation of O^-₂ centres in RbI and RbBr at low temperatures together with earlier measurements in different alkali halides suggest the following sequence of relaxation mechanisms in an unstressed srystal: Below about 3°K a one phonon tunneling process, then an activated tunneling process through the first librational state, and above 10°K a classical jumping process over the potential well.     

A procedure for one-parametric linear programming

A procedure is proposed for the parametric linear programming problem where all the coefficients are linear or polynomial functions of a scalar parameter. The solution vector and the optimum value are determined explicitly as rational functions of the parameter. In addition to standard linear programming technique, only the determination of eigenvalues is required. The procedure is compared to those by Dinkelbach and Zsigmond, and a numerical example is given.     

Negative-parity states in Pb isotopes: g-factor of the 480 ns,if Jπ = 9− isomer in 200Pb

The g-factor of the 480 ns, 9^? isomer at 2.237 MeV in ²⁰⁰Pb was measured by the time-differential perturbed angular distribution method. The result, g = ?0.0285±0.0011 confirms the rather pure $\text{(}\text{f}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}{}^{\mathrm{?1}}\text{i}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}{}^{\mathrm{?1}}\text{)}$ quasiparticle structure of this state. Half-lives of 480±20 ns, 43±3 ns and 42±4 ns have been measured for the 2237 keV 9^?, 2154 keV 7^? states in ²⁰⁰Pb and the 2208 keV state in ²⁰²Pb, respectively; E2 transitions and g-factors of negative-parity states in even, neutron-deficient Pb isotopes are discussed.     

Description of nonradiative multiphonon transitions in the static coupling scheme

Nonradiative multiphonon transitions generated by the interaction of the electronic system with quantized normal oscillation modes are described quantum-theoretically on the basis of the static coupling scheme which is an essential, physically plausible alternative model to the adiabatic coupling scheme predominantly used in earlier papers. Putting emphasis on the mathematical correctness of the calculations we obtain a generally valid expression for nonradiative multiphonon transition rates which is based on the concept of temperature-averaged overlap factors. In the case of a single phonon energy this result is reduced to very compact expressions not given in original papers published so far. For non-vanishing phonon dispersion a simple standard formula is given which is suited for approximative numerical calculations.     

Messung der Neutronenpolarisation bei der Reaktion12C(d,n 0)13N mit Hilfe der Mott-Schwinger-Streuung

The polarization of neutrons produced in the reaction¹²C(d, n ⁰)¹³N was measured. Deuterons from the Karlsruhe isochronous cyclotron were used to induce this reaction at 51,5 MeV laboratory energy. The degree of polarization was determined by using the special features of Mott-Schwinger scattering. With an uranium scatterer analysing efficiencies of up to 0.92 can be obtained at very small angles (0.23°). The analysing efficiency can be calculated if the differential cross section at 0° and the total cross section is known. These quantities were experimentally determined. The differential cross section for 49.4 MeV neutrons, scattered by uranium, was measured between 0.88° and 2.10°. By an extrapolation the value 43.4±2.6 b/sr was found for the nuclear differential cross section at zero degree. A total cross section ofσ _t=4.80±0.22 b was obtained. The neutron polarization was measured at a reaction angle of 24.5° and the result isP=?0.45±0.07. This value is fairly above the semiclassical 1/3 limit and can be only explained, if spin orbit forces are taken into account. For (d, n) reactions this is the first neutron-polarization measurement above an energy of 20 MeV.     

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Synthesis and reactions of some 3-(2-haloacyl)indoles

The reaction between indole and N-(2-haloacyl)pyridinium salts has been studied. With dioxan as solvent 1-(2-haloacyl)indole (2) was generally the product at low temperatures and 3-(2-haloacyl)indole (1) at high temperatures, as illustrated by the following α-bromopropionylation: Product ratio (1c/2a), 20° (0·01), 40° (0·8) and 60° (8·5). The fact that the a-bromobutyrylation at 60° gave 3-{N-(2-bromobutyryl)-1,4-dihydro-4-pyridyl}indole (6) as the main product, and 3-(2-bromobutyryl)indole (1d) only as a minor product, shows that the 3-acylation is affected by steric hindrance.At high reaction temperature (> 60°) the yield of1 decreased, owing to the formation of 3-indacylpyridinium salts (4).     

Spin resonant optical mixing in InSb — CW-measurements and transient effects

Optical four-wave mixing due to the resonant spin nonlinearity in n-InSb was observed in magnetic fields up to 1.4 T. The mixing of two CO-laser frequencies ω₁ and ω₂ = ω₁ - Δω yields radiation with frequencies ω₁ + 2Δω, ω₁ + Δω, ω₁ - 2Δω, and ω₁ - 3Δω. We found the resonant contribution to the third order nonlinear susceptibility arising from the spin-flip interaction to increase by more than two orders of magnitude when ω₁ is varied from 1760 cm^-1 to 1896 cm^-1. With the lasers working simultaneously Q-switched we observed radiation at ω₁ + Δω and ω₁ - 2Δω due to the mixing caused by the nonparabolicity of the conduction electrons even without an external magnetic field. At the resonant magnetic field the intensity of the mixed radiation is increased by more than one order of magnitude and is also observed when the laser pulses do not hit the sample simultaneously as long as the time difference between the two pulses does not exceed 450 ns. This points to a spin dephasing time T₂ of about 100 ns.